Production of large diameter thinwalled tubing



p 13, 1966 D. M. DOUTHETT ETAL 3,271,987

PRODUCTION OF LARGE DIAMETER THIN-WALLED TUBING Original Filed Oct. 1,1963 DRAWBENCH PUSHBENCH g 2E8 22 24w g g L; IITT'ITRI :fji'fI'j 18 Y20-: F |g.2-F

INVENTORS DELORMA M. DOUTHETT GEORGE A. MITCHELL BY I their ATTORNEYUnited States Patent 6 Claims. (Cl. 72283) This application is adivision of our copending application Serial No. 312,987, filed October1, 1963 and assigned to the assignee of the present application.

This invention relates to apparatus for producing tubing by cold-drawingtechniques, and more particularly to apparatus for the production oflarge diameter, thinwalled tubing from blooms of substantially the samediameter as the finished product but of increased wall thickness.

In the production of seamless metal tubing, 21 basic tubular shape orbloom of relatively short length and large wall thickness is initiallyproduced by a hot extrusion or hot piercing operation. This bloom isthen further Worked by rolling, swaging or more commonly by colddrawing. Of course, a tubular shape of the desired inner and outerdiameters can be produced directly by hot extrusion; however theresulting product is normally not of a quality that can be used in manyapplications because of non-concentricity, dimensional inaccuracies,rough surface finish, and softness.

All of the commonly used methods for working a thick-walled bloom toproduce the finnshed product tend to decrease the outside diameter ofthe tube, making it smaller than the size of the original bloom. Forexample, in the case of cold drawn tubing, the final outside diametermay be many times smaller than that of the origianl bloom; and as theshape is cold worked and reduced in diameter during successiveoperations, successively smaller dies must be used each time theworkpiece is drawn. Consequently, there is a direct relationship betweenthe final outside diameter of the finished product and the size of theequipment needed to produce it, the larger the final desired outsidediameter, the larger and more costly the equipment.

It is, of course, theoretically possible to produce a final producthaving an outer diameter in the range of about six inches if a bloom isoriginally employed having a starting diameter in the range of about oneto two inches larger. This, however, requires extremely large and heavyequipment and also results in an excessive scrap loss.

In an effort to increase the capabilities of a particular cold-drawinginstallation to produce larger outside diameter tubing than can bemanufactured by normal processes, arrangements have have been devisedfor eX panding the tube prior to cold working. The most conventional wayto accomplish this is to force a plug or ball through the inside of thetube, thereby enlarging both the inside and outside diameters, slightlyreducing the wall thickness, and shortening the tube. One end of theworkpiece must then be pointed or swaged on a separate machine toprovide a reduced diameter section which can be passed through the dieof a drawbench and subsequently drawn through that die to reduce itsoutside diameter. This expansion and drawing procedure may be repeatedseveral times to produce the desired finished tube outside diameter andwall thickness; however it requires three time-consuming and separateoperations and also develops a relatively high percentage of scrap dueto the length of the swaged end or point required on the large diametertube prior to drawing.

3,27l,%7 Patented Sept. 13, 1966 ice As an overall object, the presentinvention seeks to provide new and improved apparatus for producinglarge diameter thin-walled tubing from blooms having an outer diametersubstantially equal to, or even less than, that of the finished product.

More specifically, an object of the invention is to provide apparatusfor producing cold-drawn, large diameter and thin-walled tubing fromblooms of substantially the same diameter but increased Wall thickness,which apparatus overcomes the aforementioned and other disadvantages ofprior art methods.

A further object of the invention is to provide apparatus for producinglarge diameter thin-walled tubing wherein no pointing or swaging of tubeends is required prior to drawing. This not only completely eliminatesthe swaging operation but also reduces the length of the scrap end ofthe tube gripped by the draw carriage during the drawing operation.

Still another object of the invention is to provide ap paratus forproducing large diameter thin-walled tubing by cold-drawing techniqueswherein only a single die of fixed diameter is required for all drawingoperations.

In accordance with the invention, a plug is initially forced into oneend of a bloom and axially along the inner periphery of the bloom to theother end of the bloom, but not entirely therethrough, to thereby expandthe bloom and increase its inner and outer diameters except at saidother end to provide a non-expanded portion which can be passed througha drawbench drawing die. After the expansion operation, and with thetapered plug remaining in the bloom, the non-expanded diameter forwardend of the bloom is gripped by a draw carriage and the workpiece drawnthrough the die which has a diameter substantially equal to or largerthan the original diameter of the bloom prior to expansion. Thisproduces a product having an outer diameter at least equal to theoriginal diameter of the bloom, an inner diameter and length greaterthan that of the original bloom, and a wall thickness less than that ofthe original bloom. By repeating the foregoing process with plugs ofsuccessively lrager diameters, the inner diameter of the workpiece willbe gradually enlarged; however the outer diameter will remain constantfor the reason that it is always drawn through a die of the samediameter after each expanding operation. The invention, however, is notlimited to the use of a single die for all drawing operations since itmay be desirable to employ dies of different diameters to increase therange of final sizes which can be produced on a single piece ofequipment.

Further, in accordance with one embodiment of the invention, theapparatus for carrying forth the foregoing method comprises a pushbenchand a drawbench arranged in end-to-end relationship with an intermediatedie stand and common power supply. The extruded or pie-reed bloom isdropped into position on the pushbench bed, and its leading end movedagainst a stop plate mounted in position in front of the die of thealigned drawbench. Hold-down clamps are brought to bear on top of thetube and a floating-type draw plug is placed in alignment with thetrailing end of the tube. Thereafter, a long cylindrical push rodattached to a push carriage forces the plug through the inside of thetube to enlarge its inside diameter to correspond with the maximumdiameter of the tapered draw plug. The outside diameter of the tube alsogrows almost in the same proportion as the enlargement of the insidediameter; while the wall thickness and length decrease. As a specificexample, the plug may be pushed within four or five inches of theleading end of the tube; and at this point the stop plate is moved fromin front of the die and the remaining stroke of the push carriage movesthe forward end of the bloom, which has not been expanded, through thedrawing die where it is gripped by gripper jaws on a drawbench drawcarriage which moves away from the die to thereby pull the tube throughthe die while reducing its outside diameter and increasing its length.

The combination pushbench-drawbench of the invention is such that whilethe push carriage is engaged in a power stroke traveling toward the dieplate, the draw carriage is also returned toward the die plate.Thereafter, at the completion of the push stroke, the leading end of thetube is gripped by the draw carriage, which is then positioned in frontof the die plate, and the power unit is reversed. The draw carriage thenpulls the tube through the die and the push carriage is returned to itsretracted position preparatory to the next expanding operation. Thus,the time required to prepare the equipment for a subsequent expandingand drawing operation is minimized, and the equipment is simplified byvirtue of the fact that only a single prime mover is required.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIGURE 1 is a schematic illustration of one embodiment of the invention;and

FIGS. 2A-2F are diagrams showing the successive steps of operation ofthe invention.

Referring now to the drawings, and particularly to FIG. 1, thecombination pushbench-drawbench of the invention is shown and includes adie stand which carries a die 12 through which workpieces are drawn. Theworkpiece 14 comprises an extruded or pierced bloom which is clamped inposition by means of a series of hold-down clamps 16 spaced along theaxis of the bloom 14. The clamps 16 will permit expansion of the bloomduring the push stroke and serve, more or less, Only to reduce thelength-over-radius ratio and prevent buckling of the bloom during thepush stroke. In order to prevent axial movement of the bloom during anexpanding operation, a stop plate 18 is inserted between the leading endof the bloom 14 and the die 12.

In order to expand the bloom 14, a combination drawing and expandingplug 28 is forced into its right or trailing end by means of a push rod22 attached to a push carriage 24 which travels on a trackway 26. Theplug is tapered, its minimum diameter end being initially inserted intothe end of the bloom 14 followed by its maximum diameter end.

On the side of the die 12 opposite the push carriage 24 is a drawcarriage 28 which travels along a guideway or track 30. As is well knownto those skilled in the art, a draw carriage comprises a dolly or buggywhich is provided with gripping jaws adapted to engage the nonexpandeddiameter end of a workpiece, such as bloom 14, which is inserted throughthe die 12. One specific example of such gripping jaws, not shownherein, may be had by reference to US. Patent No. 2,861,679 issued to G.A. Mitchell on November 25, 1958. After the gripping jaws on the drawcarriage 28 engage the forward end of the workpiece, the draw carriageis moved away from the die, thereby pulling the workpiece through thedie while reducing its outer diameter and increasing its length. Theinner diameter of the workpiece is determined during the drawingoperation by a floating element which, in the present case, comprisesthe combination drawing and expanding plug 20 as will hereinafter beexplained.

The push carriage 24 and the draw carriage 28 are actuated by means of adouble-acting, double rod hydraulie cylinder 32. The cylinder includesa. piston 34 disposed between two variable volume chambers 36 and 38.Means, not shown, are provided for forcing fluid under pressure into oneof the variable volume chambers 36 or 38 while exhausting fluid from theother chamber whereby the piston 34 may be forced to the right or left,as the case may be.

The piston 34 is connected to two piston rods 48 and 42, the piston rod40 being connected through a clevis to a pulley or sheave 44, the pistonrod 42 being connected through a similar clevis to a pulley or sheave46. The sheaves 44 and 46 are utilized in combination with adistance-multiplying cable arrangement for the purpose of moving boththe push carriage 24 and draw carriage 28 toward or way from the die 12simultaneously. The cable arrangement includes a first cable 48 which issecured at 50 to the die stand 18. This cable passes around the sheave44 and thence around a second sheave 54 Supported on the die stand 10with the other end of the cable 48 being connected to the push carriage24 as at 56. Thus, when the variable volume chamber 38 of cylinder 32 ispressurized, the piston 34 will move to the right as viewed in FIG. 1,thereby forcing the push carriage 24 to the left. In this process, thepush rod 22 engages the plug 20 which, in turn, is forced into theinterior of the bloom 14 to expand it while increasing both its innerand outer diameters.

The push carriage 24 has connected thereto a cable 58 which passesaround a sheave 60 supported on a member 62 at the right end of theapparatus. The cable 58 is connected to the draw carriage 28 as at 64,the arrangement being such that as the push carriage 24 is moved towardthe die 12 during its power stroke when the plug 20 is forced into thebloom 14, the draw carriage 28 will also be moved along track 30 towardthe die 12 preparatory to a succeeding drawing operation. During thistime, however, the only force needed to return the draw carriage 28 tothe die that necessary to overcome the inherent weight and frictionalresistance of the draw carriage 28.

The draw carriage 28 is also connected to a cable 66 which passes aroundsheave 68 at the left end of the apparatus and thence around sheave 70on member 62 and sheave 46 to point 71 where it is anchored on themember 62. As the draw carriage 28 is moved to the right during thepower stroke of the push carriage 24, the piston 34 of cylinder 32 willmove to the right, thereby also moving sheave 46 to the right to permitthe cable 66 to follow the draw carriage 28.

During the expanding operation, the plug 20 is forced axially along theinterior of the bloom 14 to a point where it is at the left end of thebloom. In this process, the entire length of the bloom will be expandedexcept at its left end where it is not expanded due to the fact that theplug 20 has not passed through the left end of the bloom 14. At thispoint, the stop plate 18 is removed, the clamps 16 released, and thecylinder 32 actuated to move carriage 24, bloom 14 and the plug 20carried thereby to the left whereby the end of the bloom which has notbeen expanded will extend through the die 12. Thereafter, the gripperjaws on draw carriage 28 are actuated to engage the non-expanded end ofthe bloom 14; and the variable volume chamber 36 of the cylinder 32 ispressurized to thereby move both the draw carriage 28 and the pushcarriage 24 away from the die 12 in opposite directions. During thistime, the major portion of the power supplied by cylinder 32 is appliedto the draw carriage 28 which draws the bloom 14 through the die 12while reducing its outer diameter and increasing its length. The innerdiameter of the bloom 14, however, is not materially reduced due to thefact that it is controlled by the plug 20 which remains within theworkpiece as a floating drawing plug element.

If necessary to prevent collapse of the forward end of the tube whengripped by the gripper jaws of the draw carriage, an aircylinder-operated mandrel may be provided on the draw carriage which isinserted into, and supports, the forward end of the tube just prior tothe time that the gripper jaws engage the tube.

During the drawing operation, the plug 20 floats within the die openingrather than being sucked there- J through due to the relationshipbetween the lead-in angle of the die opening and the angle of thetapered surface of the plug with its axis. As is well known to thoseskilled in the art, this relationship may best be determined empirioallyfrom experimental data obtained by testing plugs of various taper anglesfor a particular die configuration.

At the completion of the drawing operation, the work piece 14 will jumpforwardly and be automatically released by the gripper jaws of the drawcarriage 28 while the plug 20 will fall out of the trailing end of theworkpiece and may be used again. At the same time, the mandrel on thedraw carriage, if employed, will be retracted from the non-expanded endof the bloom to permit it to fall into a receiving trough in accordancewith usual drawbench practice. Following the drawing operation, theworkpiece 14 is returned to the clamps 16, and a plug of larger maximumdiameter is forced into the workpiece 14 to repeat the foregoingprocess. That is, the inner and outer diameters of the workpiece 14 areagain expanded, but during the succeeding drawing operation the outerdiameter of the workpiece is reduced to its original value, assuming thesame-sized die is used. By utilizing successive floating plugs 20 ofprogressively larger maximum diameters, it will be appreciated that theend result is a tube having an inner diameter much larger than that ofthe original bloom 14, but an outer diameter slightly larger than thatof the bloom 14, with the overall length of the workpiece beingincreased.

Operation of the apparatus shown in FIG. 1 may best be understood byreference to FIGS. 2A-2F. Thus, the starting positions of the variouselements are shown in FIG. 2A with the draw carriage 28 and pushcarriage 24 being at their positions furthest removed from the die 12.The bloom 14 is positioned between the end of push rod 22 and the die12; the plug 20 inserted into the right end of the bloom 14; and thestop plate 18 inserted between the die 12 and the left end of bloom 14.At this time the bloom 14 has an outside diameter OD-l, and a relativelysmall inside diameter ID-l. Plug 20 has a minimum diameter portion 21which is initially inserted into the bloom 14, a tapered portion 23 anda maximum diameter portion 25 of diameter larger than the inner diameterID-1 of the bloom.

As the push carriage 24 is forced toward the die 12, it will also forcethe plug 20 into the interior of the bloom 14 as shown in FIG. 2B, withthe draw carriage 28 being moved toward the die 12 at the same time. Inthis process, both the inner and outer diameters of the bloom 14 areincreased. Thus, the outside diameter of the bloom is now OD-2 and theinside diameter is ID-2, which is substantially of the same diameter asportion 25 of plug 20. The plug 20, however, is not forced through theentire length of the bloom 14 but stops in the position shown in FIG. 2Bto provide a section 72 at its left end which is not expanded and has anouter diameter equal to OD-l. Following this step, the stop plate 18 isremoved and the push carriage 24 and draw carriage 28 moved furthertoward the die 12, thereby forcing the non-expanded end 72 of the bloom14 through the die where it is gripped by gripper jaws on the drawcarriage 28. The cylinder 32 is now reversed and the draw carriage 28moves away from the die, thereby pulling the workpiece or bloom 14through the die while decreasing its outer diameter and increasing itslength as shown in FIGS. 20 and 2D. The inside diameter of the expandedbloom 14, however, is not materially decreased due to the fact that theplug 20 remains in the bloom during the drawing operation and controlsthe inner diameter. This operation continues until a point is reached asshown in FIG. 2B where the plug 20 drops out of the end of the drawnbloom 14, and the bloom is released by the gripper jaws of the drawcarriage 28. The product now has an outside diameter slightly largerthan the original outside diameter OD-l but an inside diameter ID-3which is somewhat less than the diameter ID2 but larger than theoriginal inside diameter ID-l. The overall effect, therefore, has beento materially increase the inner diameter and length of the workpiecewhile only slightly increasing its outside diameter.

In FIG. 2F, the relationship of the parts are the same as those shown inFIG. 2A; however in this case a plug 20-1 of larger maximum diameter isforced into the right end of the bloom 14. This, of course, will createan inside diameter larger than ID-3 and also an increased outerdiameter. In the subsequent drawing operation, however, the outsidediameter is again reduced to slightly larger than OD-l, but the insidediameter remains larger than ID-3. This process is repeated as manytimes as necessary in order to produce the required inside diameter andwall thickness.

Although the invention has been shown in connection with a certainspecific embodiment, it will be readily apparent to those skilled in theart that various changes in form and arrangement of parts may be made tosuit requirements without departing from the spirit and scope of theinvention. In this respect, it will be apparent that by providing a diehaving a diameter materially larger than that of the original bloom, afinal product can be produced which will also have a larger outsidediameter for the reason that the bloom is always expanded during thepush stroke. Furthermore, it will be appreciated that in an actualproduction operation, a plurality of blooms will be processed with thesame sized plug followed by processing of all blooms by the next-largerplug rather than completing all expanding and drawing operations on asingle workpiece before proceeding with the next.

We claim as our invention:

1. In apparatus for producing tubular shapes by expanding a tubularbloom followed by drawing the bloom, the combination of a drawing die, adraw carriage movable toward and away from the die on one side of thedie, means for forcibly moving said drawn carriage away from said die, apush carriage movable toward and away from the die on the other side ofthe die in alignment with said draw carriage, means for positioning atubular bloom to be expanded between the push carriage and the die whenthe push carriage is at a point removed from the die, an expanding plugadapted to be forced through said bloom, means for moving the pushcarriage toward the die whereby the push carriage will force saidexpanding plug into said bloom to effect an expanding operation on saidbloom, and means for forcibly moving said draw carriage away from thedie whereby the draw carriage effects a drawing operation on the bloomafter it has been initially expanded.

2. The combination of claim 1 including means for simultaneously movingboth the draw carriage and the push carriage toward or away from thedie.

3. The combination of claim 2 wherein said means for simultaneouslymoving both the draw carriage and the push carriage comprises a sheavepositioned at one end of the apparatus, and a cable-like element whichpasses around said sheave and is connected at its opposite ends to thedraw carriage and said push carriage.

4. The combination of claim 2 wherein said means for simultaneouslymoving both the draw carriage and the push carriage comprises a firstsheave positioned at one end of the apparatus, a cable element whichpasses around said sheave and has one end connected to said drawcarriage and its other end connected to the push carriage, adouble-acting double piston rod hydraulic cylinder assembly, meansincluding a distance-multiplying sheave and cable arrangement connectingone of said piston rods to said push carriage, and means including asecond sheave and cable arrangement connecting the other of said pistonrods to said draw carriage, the arrangement being such that actuation ofthe hydraulic cylinder in one direction will force the push carriage anddraw carriage toward the die while actuation in the opposite directionWill cause movement of the push carriage and draw carriage away from thedie.

5; The combination claimed in claim 1 and including a removable stopplate positioned at the forward end of the bloom for preventing forwardmovement of the bloom as the push carriage moves toward the die duringan expanding operation.

6. The combination claimed in claim 1 wherein said die has a perimeterof dimensions at least as large as the outer perimeter of dimensions ofthe bloom when expanded, and including means for stopping said pushcarriage in its movement toward the die after it has expanded all butthe forward end of the bloom.

References Cited by the Examiner UNITED STATES PATENTS 2,23 4,863 3/1941 Heetkamp 723 70 CHARLES W. LANHAM, Primary Examiner.

H. DIETER HOINKES, Examiner.

1. IN APPARTUS FOR PRODUCING TUBULAR SHAPES BY EXPANDING A TUBULAR BLOOMFOLLOWED BY DRAWING THE BLOOM, THE COMBINATION OF A DRAWING DIE, A DRAWCARRIAGE MOVABLE TOWARD AND AWAY FROM THE DIE ON ONE SIDE OF THE DIE,MEANS FOR FORCIBLY MOVING SAID DRAWN CARRIAGE AWAY FROM SAID DIE, A PUSHCARRIAGE MOVABLE TOWARD AND AWAY FROM THE DIE ON THE OTHER SIDE OF THEDIE IN ALIGNMENT WITH SAID DRAW CARRIAGE, MEANS FOR POSITIONING ATUBULAR BLOOM TO BE EXPANDED BETWEEN THE PUSH CARRIAGE AND THE DIE WHENTHE PUSH CARRIAGE IS AT A POINT REMOVED FROM THE DIE, AN EXPANDING PLUGADAPTED TO BE FORCED THROUGH SAID BLOOM, MEANS FOR MOVING THE PUSHCARRIAGE TOWARD THE DIE WHEREBY THE PUSH CARRIAGE WILL FORCE SAIDEXPANDING PLUG INTO SAID BLOOM TO EFFECT AN EXPANDING OPERATION ON SAIDBLOOM, AND MEANS FOR FORCIBLY MOVING SAID DRAW CARRIAGE AWAY FROM THEDIE WHEREBY THE DRAW CARRIAGE EFFECTS A DRAWING OPERATION ON THE BLOOMAFTER IT HAS BEEN INITIALLY EXPANDED.